Extrusion apparatus for forming thin-walled honeycomb structures

ABSTRACT

Apparatus for forming thin-walled honeycomb structures is provided in the form of an extrusion die having an outlet face provided with a gridwork of interconnected discharge slots and an inlet face provided with a plurality of feed openings extending partially through said die in communication with said discharge slots. Extrudable material is fed to said die under pressure wherein the extrudable material flows longitudinally through the feed openings in the inlet face of the die and is directed thereby to the interconnected discharge slots communicating with the outlet face, wherein a portion of the material flows laterally within such slots to form a continuous mass before being discharged longitudinally therefrom to thereby form a thinwalled structure having a multiplicity of open passages extending therethrough.

"United States Patent [191 Bagley [4 1 Sept. 16, 1975 [75] Inventor:Rodney D. Bagley, Corning, N.Y.

[73] Assignee: Corning Glass Works, Corning,

[22] Filed: July 27, 1973 [21] Appl. No.: 383,388

Related US. Application Data [62] Division of Ser. No. 196,986, Nov. 9,1971, Pat. No.

[52] US. Cl. 425/464; 425/382; 425/467 [51] Int. Cl. B29F 3/04 [58]Field of Search 264/176 F, 177 R, 177 F;

425/131, 461, 467, 462, 463, 465, 466, 464, 67, 71, 72, DIG. 217, 382

Kilsdonk 425/464 X Gaffi-iey 425/131 X Primary ExaminerRobert D. BaldwinAssistant ExaminerMark Rosenbaum Attorney, Agent; or Firm-Burton R.Turner; Clarence R. Patty, Jr.

[ ABSTRACT Apparatus for forming thin-walled honeycomb structures isprovided in the form of an extrusion die having an outlet face providedwith a gridwork of interconnected discharge slots and an inlet faceprovided with a plurality of feed openings extending partially throughsaid die in communication with said discharge slots. Extrudable materialis fed to said die under pressure wherein the extrudable material flowslongitudinally through the feed openings in the inlet face of the dieand is directed thereby to the interconnected discharge slotscommunicating with the outlet face, wherein a portion of the materialflows laterally within such slots to form a continuous mass before beingdischarged longitudinally therefrom to thereby form a thin-walledstructure having a multiplicity of open passages extending therethrough.

PATENTEU l 5 [975 3. 905 743 SHEET 2 BF 3 szam 3 u; 3

PATH-NEE SE? 1 6 i975 EXTRUSION APPARATUS FOR FQRMING THIN-,WALLEDHONEYCOMB STRUCTURES This is a division of application Ser. No. 196,986,filed Nov. 9, 1971, now, U.S. Pat. No. 3,790,654.

BACKGROUND OF THE INVENTION This invention pertains to the art ofmanufacturing thin-walled honeycomb structures from extrudable materialsuch as ceramic batches, molten glasses, plastics, molten metals, andsimilar materials which have the property of being able to flow orplastically deform during extrusion while being able to becomesufficiently rigid immediately thereafter so as to maintain structuralintegrity. More particularly, the present invention relates to animproved extrusion die structure and method for forming uniformthin-walled cellular or honeycomb type articles having a plurality ofopenings or passages extending therethrough with wall portions betweensuch openings having a preferred thickness of between about 0.002 and0.050, so as to provide open frontal areas of about 75% or greater.

As pointed out by the prior art in U.S. Pat. No. 3,1 12,184, it has beenknown to make thin-walled ceramic honeycomb structures for use inregenerators, recuperators, radiators, catalyst carriers, filters, heatexchangers, and the like by coating a carrier with a ceramic slurry andbinder mix and flowing crimped and flat sheets of such coated carriertogether to make a cellular type structure. Although suitable productsmay bev formed in this manner, the prior art technique has not beencompletely'satisfactory due to the fact that cell shape is limited andwall thicknesses may not be uniform, and further the process isrelatively slow and requires costly materials.

A further U.S. prior art Pat. No. 3,406,435 discloses apparatus formanufacturing ceramic elements having a honeycomb structure wherein aplurality of elongated thin-walled sleeve members having extensions withclosed end portions are connected to an extruder cylinder. The materialto be extruded is forced through the elongated sleeve members andoutwardly through orifices formed in side walls of the extensionsattached thereto. The sleeve extensions are spaced from each other toprovide channels in which the material from the orifices become reshapedinto a honeycomb structure.

Although the structure of U.S. Pat. No. 3,406,435 appears to overcomesome of the problems associated with atypical die assembly such as shownin U.S. Pat. No. 1,849,431 wherein a spider or cross-head positions aplurality of rods, one for each core or cell in the article to beformed; the apparatus is not completely satisfactory for producinghoneycomb structures having a multiplicity of sized cells or openings,since not only would it be virtually impossible to construct due to thenumber of sleeves required, but also the unsupported extensions on suchsleeves would have a tendency to distort under extrusion pressures. Inaddition, as shown in the patent drawings, truly thin-walled structuresare not obtainable'with such a structure. Further, any variation in thespaces between the extensions will tend to result in a curved extrusionor rippling of the formed article, since a thicker section of the wallwill extrude more rapidly than a thin section.

Accordingly, the present invention has overcome the problem ofsuspending a plurality of core members in predetermined spaced apartrelationship, which has plagued the prior art, by providing a completelyunique manner of forming an extrusion die with uniform discharge slotswhich are maintained in substantially rigid orientation duringextrusion.

7 SUMMARY OF THE INVENTION In its very simplest form, the presentinvention is directed to an improved extrusion die structure for formingthin-walled cellular or honeycomb structures and to the method offorming such structures. Cellular or honeycomb structures refer to anystructure having a plurality of openings or passages of any desired sizeor shape extending therethrough, whereas thin walls refers to the wallsbetween such openings or passages having a thickness of between about0.002 and 0.050. The extrusion die per se, is preferably made ofaunitary construction having a plurality of interconnected dischargeslots provided with uniform openings in the out let face of the die. Thedischarge slots may either be uniformly spaced-apart or formed withvariable spacing therebetween if desired, and the gridwork formed in theoutlet face by such slots may be of virtually any geometric pattern suchas square, rectangular, triangular, hexagonal and circular. A pluralityof feed openings or passageways communicate between the inlet face ofthe die and inner root portions of the discharge slots to deliverextrudable material from an extrusion chamber to the discharge slots.The feed passageways may be in the form of slots or holes whichintersect selected portions of the gridwork formed by theinterconnecting discharge slots.

The discharge slots, which are of a predetermined size and orientationto form a desired thin-walled structure, extend inwardly from the outletface a distance sufficient to insure the lateral filling of all outletportions of such slots with the extrudable material delivered thereto bythe feed holes, prior to such material being discharged from the die. Inorder to facilitate such lateral flow of batch material within thedischarge slots so as to provide a coherent mass of such material withinthe gridwork formed by the interconnected discharge slots, the dischargeslots are preferably formed with a greater resistance to batch flow thanthat provided by the feed passageways. However, the resistance to flowin the slots need not necessarily be greater than that in the feedpassageways, but must be sufficient to insure that the batch materialwill flow laterally together within the depth of the discharge slots andprior to discharge therefrom so as to form a continuous mass ofinterconnected batch prior to such discharge. Further, the root portionsof such discharge slots may be contoured to provide ease in lateralflow.

Although the die body is preferably produced as a unitary constructionso as to provide the required strength and rigidity to withstandextrusion pressures without failure or deliterious deformation, the bodyper se may be formed either from a single piece of material or from aplurality of pre-formed sheets which are subsequently fused or bondedtogether to form a unitary body. However, where the extrusion pressuresare not excessive, such sheets may merely be clamped together. A collarmember may be provided about the die body to form a bounding passageabout the periphery of the outlet face, so as to provide for an integralshell about the honeycomb structure. A plurality oflongitudinally-extending feed openings are formed in the die assembly tofeed batch material to the annular passage, and restriction means may beprovided to vary the resistance to flow through such passage.

It thus has been an object of the present invention to provide a novelrelatively easily manufacturable extrusion die structure for formingthin-walled honeycomb articles having a plurality of openings percrosssectional area, wherein said die structure is substantially rigidso to maintain dimensional stability during extrusion and therebyprovide uniform thin walls between such openings.

A further object of the invention has been to provide an improved methodof forming thin-walled honeycomb articles by delivering extrudablematerial longitudinally through feed passages to a plurality ofinterconnected discharge slots forming a gridwork, impeding the flowthrough such slots and laterally flowing a portion of the materialdelivered to such slots to form a unitary grid-like mass, thenlongitudinally discharging said mass to form a honeycomb structure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a dieassembly embodying the present invention.

FIG. 2 is an elevational view in section taken along line 2-2 of FIG. 1.

FIG. 3 is a bottom plan view of the die assembly shown in FIG. 1.

FIG. 4 is a greatly enlarged fragmental top plan view of the embodimentshown in FIG. 1 illustrating the orientation between the feed openingsand discharge slots.

FIG. 5 is a top plan view of a further embodiment.

FIG. 6 is a top plan view of an additional embodiment.

FIGS. 7, 8 and 9 are fragmental cross-sectional views in elevationillustrating various forms of discharge slots which may be utilized withthe disclosed die structures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,and particularly FIGS. 1 through 4 inclusive, a die assembly 10 is showncomprising a die body 12 and a collar 14. The die body has an inlet face16 provided with a plurality of openings or feed passageways 18 forfeeding batch material I to the matrix of a honeycomb structure, as wellas a plurality of annularly arranged feed passages 20 for feeding batchmaterial to an outer casing or shell for such structure. If desired, acircular feed slot could be substituted for the feed passages 20, andthe resulting central die portion held in position by suitable pins orthe like.

The die body 12 has an outlet face 22, opposite inlet face 16, which isprovided with a plurality of interconnected discharge slots 24. As shownin FIG. 3, the interconnected discharge slots 24 form a gridwork throughwhich the batch material is extruded to form the matrix of a coherenthoneycomb structure. Each discharge slot 24 is provided with a rootportion 26 at its inward most end, and the feed passageways 18communicate with selected areas of such root portions. As shown in FIG.4, the feed passageways 18 may be in the form of holes which communicatewith alternate intersecting slots formed in the discharge gridwork, suchthat the feed holes intersect one set of diagonal corners of core pins28 formed by the intersecting slots.

As shown particularly in FIG. 2, the feed holes 18 have a taper 30 attheir lower ends which intersect the root portions 26 of slots 24. Therelatively large area of intersection as shown in'FIG. 4 helps toprovide for lateral flow within the slots between the intersectionsthereof with adjacent feed holes 18, so as to completely fill thelateral extent of the slots with batch material prior to the dischargethereof from the slots, even though a portion of the batch materialdirectly below the feed holes longitudinally flows directly through suchdischarge slots. The discharge slots 24 extend inwardly a sufficientdistance to insure the filling of at least the outlet end of the slotsthrough lateral flow of the batch material prior to the dischargethereof from the gridwork formed by such slots. The resistance to batchflow necessary for encouraging lateral flow will of course not only beaffected by the viscosity of the extrudable material, but also by thedepth of the slots through which such material must travel during itsobtainment of lateral flow. Preferably the resistance to batch flow inthe slots should be at least equal to that in the feed holes, however,satisfactory results have been obtained by providing the slots with fromabout 0.8 to 6 times the resistance to flow through the feedpassageways.

As shown particularly in FIG. 2, collar member 14 may have an adjustableinsert 32 threadably attached thereto. The lower inner periphery ofinsert 32 forms an annular orifice 34 with the outer periphery of outletface 22. Feed passages 20 supply batch material to the annular orifice34 to provide an intergral casing or shell about the honeycomb matrixformed by the gridwork of discharge slots 24. The adjustable insert 32has an upper tapered surface 36 which cooperates with outwardly taperedsurface 38 formed on die body 12, to vary the resistance to the flowtherebetween of batch being fed to the annular orifice 34. That, is, theresistance to the flow of batch material being delivered to the annularorifice 34 may be varied by threadably adjusting the position of insert32 within collar 14. Not only do the tapered surfaces 36 and 38 providea means for varying the resistance to flow, but also permit the annularring of feed passages 20 to be outwardly offset and thereby permit thepositionment of a full complement of feed passageways 18 for uniformlyfeeding batch material to the gridwork of interconnected slots 24.

Although a rectangular gridwork is shown being formed by discharge slots24 in FIGS. 3 and 4, the core pins 28 formed by slots 24 may be of asquare configuration as shown in FIG. 5. Further, if desired eachintersecting slot 24 may be provided with a feed hole 18 as shown inFIG. 5, rather than at every other intersection as shown in theembodiment of FIG. 4. The gridwork formed by the intersecting slots maybe of virtually any desired pattern, including such geometric shapes asround, square, oblong, triangular, or hexangular. Honeycomb structuresfor use as heat exchangers, for instance, may be in the form of longthin passages formed by a plurality of thin parrallel walls having onlyperiodic perpendicular webbing walls for maintaining the spacing betweensuch parallel walls.

As shown in the additional embodiment of FIG. 6, the discharge slots 24may be fed by feed passageways 18 in the form of longitudinal slots,rather than by circular holes as shown in the embodiments of FIGS. 4 and5. It will be apparent, however, that the feed slots 18 formed intheinlet face of the die body shown in FIG. 6 must be out of registerwith the discharge slots 24 formed in the outlet face, so that the baseof the core pins 28 formed by the intersecting slots is not weakenedexcessively. Accordingly, it is felt that although feed slots may beutilized if desired, feed holes have an advantage over feed slots sincea more ,rigid structure is usually obtained. As previously mentioned,the feed holes need only to be located such that the feed to the slotsis uniform, since the extrudable material must flow laterally from thefeed holes to completely fill the slots in the die prior to dischargefrom the outlet face. i I i Referring now to FIGS. 7, 8 and 9, variousforms of slot configurations are 'shown which may be utilized with thedie structures of the present invention. Although the various slotconfigurationsmay be formed in a unitary die block by applyingconventional machining and cutting techniques, or through 'the use ofelectric discharge machining, the slots are illustrated as being formedin a plurality of sheets which may be individually machined, stackedtogether, and then formed into a unitary body'such as byclamping,'brazin'g, or diffusion bonding. Similarly, their associatedfeed holes may be formed either before or after bonding. Slot 24a, isshown in Fig. 7 as being equally formed iiitwo opposing sheets 40, insuch a manner so that the root portion 26 has a larger cross sectionthan'the same cross section of the discharge-opening in outlet face 22,and the opposed sidewalls gradually taper inwardly from the root portionto the outlet face.

. In a like manner, FIG. 8 illustrates a slot'24b being equally formedin opposing sheets 40 and having an enlarged root portion 26 as comparedwith the discharge opening in outlet face 22. However, the opposed sidewalls of the slot 24b initially taper inwardly from the root toward theoutlet face but have a parallel section adjacent such outlet face. FIG.9 illustrates a slot configuration 24c wherein one wall of the slot isformed by an uncut wall of a sheet 40 whereas the opposite wall isformed with a taper and is formed in an adjacent sheet 40. If desired,theslot 24c could be provided with a parallel opposing wall portionadjacent the outlet face 22. Further, any of the slots 24, 24a, 24b, or240 or their associated feed holes could be formed within a unitary orlaminated die body by means of chemical machining as disclosed in U.S.Pat. Nos. 2,628,160, 2,684,911, and 2,971,853. Such chemical machiningwould also be useful in forming a plurality of intersecting circulardischarge slots.

The particular material utilized to produce the die body will of coursebe predicated upon the material to be extruded therethrough. The dies,for example, may be manufactured from machinable metals such as aluminumand cold rolled steel, or vitreous and ceramic materials such as glassceramics, tungsten carbide and alumina. Although the utilization ofslots having con toured roots for facilitating the lateral flow of batchmaterial therewithin has been disclosed, it has been found thatstraight-sided slots 24 as shown in FIG. 2 are very adequate forextruding ceramic batch materials.

As will be noted in FIG. 3, some of the core pins 28 about the peripheryof the outlet face 22 are of a reduced size due to the circularconfiguration of annular orifice 34. However, by shaping the outsidecasing produced by orifice 34 so that wall portions thereof are parallelto the slots formed in the outlet face, all of the core pins may then beformed of an equal size. For example, if the orifice 34 is formed with asquare opening,

and the outlet face is provided with a gridwork having a square slotpattern, all. of the core pins may be of equal size. Further, if-theorifice 34 is provided with a hexagonal opening and a triangular slotpattern is formed in the outlet face of the die, all of the core pinswill be of equal size since the gridwork will coincide with the casingconfiguration.

,Although the feed holes 18 are usually uniformly drilled within the diebody to intersect with selected areas of the slotsforming the dischargegridwork, the diameters of the various feed holes may be varied inselected areas to provide greater or less feedas may be necessary due tothe particular configuration of the extruded cellular honeycomb article.Even though the utilization of longitudinally extending feed holes ispreferred, it may be desirable to slant feed holes in the area of thecollar in order to provide complete batch filling adjacent the casing.Further, although the invention is primarily useful' in overcoming theproblems of forming thin-walled honeycomb structures having from about60 to 600 openings per square inch of cross sectional area, it should beappreciated that it may also be used in making thick walls if desired.

It will be readily apparent to those skilled in the art that theparticular size and shape of individual orifices embodying the ,presentinvention will vary with the physical properties of the material beingextruded, and although the-presentinvention is not directed toextrudable batch materials per se, but rather to a method and apparatusfor extruding honeycomb articles, the following specific example isgiven merely as being one illustration of the invention;

A 5 inch diameter die having an overall thickness of 1.2 inch was madefrom cold rolled steel and provided with a surrounding collar member. Agridwork of discharge slots was cut into the outlet face thereof with awidth of 0.010 inches and a depth of 0.150 inches forming square corepins having a width of 0.065 inches. Feed holes having a diameter of0.081 inches were drilled into the inlet face of the die to a depth of1.05 inches so as to intersect the discharge slots adjacent every otherintersection of the gridwork, thus producing 89 feed holes per squareinch of cross-sectional area. The slots had a relative resistance toflow of about 4 times that produced by the feed holes. Also a circle offeed holes for the shell or outer casing were drilled with a diameter of0.070 inches and a depth of 0.900 inches to form a total of 72 feedopenings for feeding batch to the annular orifice formed between the diebody and collar member.

A ceramic batch material comprising about 58 parts by weight ofpulverized EPK Florida Kaolin, obtainable from Whittaker, Clark andDaniels of New York, N.Y., about 20 parts by weight of Texas white talcNo. 2619, obtainable from Hamrnel & Gillespie, Inc. of White Plainfield,N. .I., about 22 parts by weight of T-6l alumina produced by AluminumCorp. of America, and about 28 parts by weight of water, with suitableextruding aids for bonding and plasticizing such as methyl cellulose,was fed to the die under a pressure of about 1900 psi at an extrusionrate of about 45 inches per minute. The batch material flowedlongitudinally through the feed passages and was delivered to theinterconnected discharge slots forming the squarepatterned gridwork,whereupon a portion of the material flowed laterally within the gridworkto form a continuous grid-like mass therewithin. Batch wassimultaneously fed to the annular orifice surrounding the gridlike mass,and then the interconnected mass was longitudinally dischargedsimultaneously from said slots and said orifice to form a honeycombstructure with an integral casing. The resulting structure had 179openings per square inch with wall members therebetween of 0.010 inches,thus producing an open frontal area of about 75%. Both the cells and thebounding wall members were uniform throughout their cross-sectional andlongitudinal extents. It will be appreciated, that after the ceramicstructure was dried and fired, the resulting wall members had athickness of even less than 0.010 inches thus resulting in a trulythin-walled honeycomb structure having both uniform wall portions andcells.

Although the now preferred embodiments of my invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications may be made thereto without departing from thespirit and scope thereof as defined in the appended claims.

What is claimed is:

1. Apparatus for forming honeycomb articles which comprises:

A. a plurality of sheets of material each having opposed faces boundedby top and bottom edges;

B. a plurality of said sheets each having a groove of said dic;

E. said extrusion die having a die body provided with an inlet face andan outlet face;

F. a plurality of feed passageways formed in said inlet face andextending longitudinally inwardly within said die body parallel to theaxis of extrusion;

G. said grooves open to said bottom edge of said sheets of materialproviding a plurality of interconnected dishcarge slots in said outletface which extend inwardly along said adjacent faces into communicationwith inner ends of said longitudinal feed passageways; and

H. said discharge slots having means for providing resistance to batchflow which is sufficient to insure that the batch material will flowlaterally together within the depth of said discharge slots.

-2. Apparatus for forming honeycomb articles as defined in claim 1wherein the adjacent faces of a pair of stacked sheets of said materialare each provided with one of said grooves which is open to said bottomedge and closed to its opposed face, and said grooves within saidadjacent faces being juxtapositioned to complementally form a contoureddischarge slot.

3. Apparatus for forming honeycomb articles as defined in claim 1including:

A. a unitary die formed from laminated sheets of material; 1 B. saidlaminations extending substantially perpendicular to said inlet andoutlet faces; and

C. said plurality of feed passageways extending inwardly of the die bodyalong said laminations to communicate with said discharge slots formedin the outlet face of said die body.

1. Apparatus for forming honeycomb articles which comprises: A. aplurality of sheets of material each having opposed faces bounded by topand bottom edges; B. a plurality of said sheets each having a grooveformed in one of said opposed faces, open to said bottom edge, andclosed by the other of said opposed faces; C. additional grooves formedin said sheets open to said bottom edges and open at least to one ofsaid opposed faces of such sheets; D. said sheets being stacked togetherto form a unitary extrusion die with adjacent faces of said stackedsheets lying parallel to the axis of extrusion of said die; E. saidextrusion die having a die body provided with an inlet face and anoutlet face; F. a plurality of feed passageways formed in said inletface and extending longitudinally inwardly within said die body parallelto the axis of extrusion; G. said grooves open to said bottom edge ofsaid sheets of material providing a plurality of interconnecteddishcarge slots in said outlet face which extend inwardly along saidadjacent faces into communication with inner ends of said longitudinalfeed passageways; and H. said discharge slots having means for providingresistance to batch flow which is sufficient to insure that the batchmaterial will flow laterally together within the depth of said dischargeslots.
 2. Apparatus for forming honeycomb articles as defined in claim 1wherein the adjacent faces of a pair of stacked sheets of said materialare each provided with one of said grooves which is open to said bottomedge and closed to its opposed face, and said grooves within saidadjacent faces being juxtapositioned to complementally form a contoureddischarge slot.
 3. Apparatus for forming honeycomb articles as definedin claim 1 including: A. a unitary die formed from laminated sheets ofmaterial; B. said laminations extending substantially perpendicular tosaid inlet and outlet faces; and C. said plurality of feed passagewaysextending inwardly of the die body along said laminations to communicatewith said discharge slots formed in the outlet face of said die body.